Magnetic memory disks are commonly utilized as storage media, such as, for example, as hard drives in computers. Such magnetic memory disks typically consist of ceramic substrate plates which are ground to the precise dimensions required for the particular application involved.
Magnetic memory disks are usually required to be produced with extremely high tolerances for flatness, surface, and edge quality. This is particularly true in computer hard disk applications, where the magnetic memory disk spins very close to the magnetic read/write recording heads. Consequently, to produce memory disks which satisfy these requirements, precision grinding and machining techniques are utilized to shape the disks.
One such grinding and machining technique involves the use of a high-precision turning lathe. During this operation, the disks are typically fastened to the face of a chuck by applying a vacuum from the chuck to the disk.
Examples of such vacuum holding apparatus are disclosed in U.S. Pat. No. 3,729,206 to Cachon et al. and U.S. Pat. No. 4,671,147 to Fehrenbach et al. These patents disclose holding the substrate disks onto the chuck by providing the chuck with concentrically arranged annular grooves or holes which are connected to a vacuum source. By applying a vacuum to the substrate plate via the holes or grooves in the face of the chuck, the substrate plate is held in place during the grinding operation. However, such vacuum chucks have not been able to consistently provide enough force to retain the disk during all types of machining operations. Consequently, efforts have been made to improve them. U.S. Pat. No. 4,603,867 to Babb et al. discloses a vacuum chuck wherein the applied vacuum force is improved by providing an O-ring on the peripheral edge of the chuck between the chuck and the disk.
Unfortunately, vacuums can typically only be applied at pressures of less than about 1 atmosphere. Even when applied very efficiently, this relatively low pressure is not always sufficient to maintain the disk against the chuck during machining operations, such as, for example, edge grinding operations. Further, as the outside diameter of the memory disk is ground down, the surface area available for exposure to the vacuum chuck gets smaller, thereby further increasing the difficulty in applying an adequate vacuum.
The present invention is directed to an apparatus and method for grinding magnetic memory disks which avoids the deficiencies of prior art grinding processes.